A construction machine (a kind of work machine) in a form of a wheeled hydraulic excavator (simply referred to as a “hydraulic excavator” hereinafter) that is capable of running on public roads has been known. Such a hydraulic excavator is powered by an engine (e.g. a diesel engine) to be adapted to drive a travelling mechanism for traveling and to actuate working equipment for excavation work and the like. When fuel consumption of such a hydraulic excavator is to be analyzed, fuel consumption when the working equipment attached to a vehicle body of the hydraulic excavator is working (referred to as a “work mode” hereinafter”) and fuel consumption when the hydraulic excavator is autonomously travelling for moving the hydraulic excavator (referred to as a “street mode” hereinafter) have to be separately considered. Since there is a large difference between the fuel consumption during the work mode and the fuel consumption during the street mode, the fuel consumption in the respective operation modes has to be separately evaluated for determining the fuel-efficiency/inefficiency of the hydraulic excavator. In other words, since a load applied on the engine (i.e. use range of engine output) differs between the work mode and the street mode, fuel amount consumed by the engine (average fuel consumption) differs between respective operation modes.
In recent years, in response to a growing demand for energy saving on work machines, some of construction machines include a display unit that is mounted in an operator's cab of a work machine and is adapted to graphically display information representing a variation in fuel consumption or information indicating past results of the fuel consumption. On the other hand, when fuel consumption is to be graphically displayed on a fuel-consumption indicator of such a display unit, a target fuel-consumption line indicating a border corresponding to target fuel consumption is sometimes displayed on the fuel-consumption indicator in order for an operator of the work machine to recognize whether the actual fuel consumption is within the target fuel consumption or not. With the status of the fuel consumption being displayed on the fuel-consumption indicator in the above-described format, the operator can visually recognize the actual fuel consumption and the target fuel-consumption line and is inclined to perform a drive operation (i.e. an operation for work or travelling) so as to keep the fuel consumption under the target fuel-consumption line. Since the target fuel-consumption line is displayed on the display unit, the operator keeps a drive operation for economical work or travelling in mind.
Incidentally, since the average fuel consumption largely differs between the street mode and the work mode as described above, the target fuel consumption also differs in the respective operation modes. Accordingly, the fuel-consumption indicator of the display unit on which the fuel consumption is to be displayed has to be provided with separate target fuel-consumption lines corresponding to each of the operation modes.
However, even when one tries to separately provide the fuel-consumption indicators on the display unit corresponding to each of the operation modes, there is a limitation of allowable area capable of being occupied by the fuel-consumption indicator on the display unit. The display unit mounted in a work machine not only displays the fuel consumption but also notifies to an operator or a serviceman a cooling-water temperature of the engine of the work machine, a hydraulic oil temperature for hydraulically driving the traveling mechanism or working equipment, residual fuel level, cumulative operation time of the work machine (service meter), various abnormality information and the like. Further, since the operator of the work machine performs an operation while looking at a work site outside the operator's cab, it is not desirable for the display unit mounted in the operator's cab to be sized to block the operator's view. Thus, when the fuel-consumption indicators are separately provided on the display unit corresponding to each of the operation modes, the display area for the above-mentioned various information become small, thereby deteriorating visibility.
An attempt for displaying the fuel consumption in the respective operation modes on a single fuel-consumption indicator would cause a different problem due to the above-described difference in the target fuel consumption in the respective operation modes. In general, the average fuel consumption in the work mode is smaller than the average fuel consumption in the street mode (i.e. less fuel is consumed per a unit time in the work mode), so that the target fuel consumption in the work mode becomes smaller than the target fuel consumption in the street mode.
If the target fuel consumption or the target fuel-consumption line displayed on the display unit is designed primarily in consideration of the work mode, fuel consumption larger than the work mode is displayed during the traveling in the street mode, so that the operator is obliged to view the fuel consumption level larger than the target fuel consumption depending on the traveling condition. Accordingly, the operator viewing the display unit cannot perform a drive operation for economical driving in view of the display of the actual fuel consumption relative to appropriate target fuel consumption in the street mode.
On the other hand, if the target fuel consumption or the target fuel-consumption line is designed primarily in consideration of the street mode, fuel consumption smaller than the street mode is displayed during the operation in the work mode, so that the operator is obliged to view the fuel consumption level smaller than the target fuel consumption depending on the working condition. Thus, the operator viewing the display unit assumes that the operation can be performed within the target fuel consumption even with slightly larger fuel consumption, so that the operator performs an operation that exceeds the originally intended target fuel consumption during the work mode, thereby failing to perform a drive operation for economical work.
In view of the above, a display unit that is adapted to change the setting of the target fuel consumption as desired with a single fuel-consumption indicator (eco gauge) has been proposed (see Patent Literature 1). With the above display unit, the display screen can be switched to a target-setting screen by a predetermined display operation and the target fuel consumption can be changed in the target-setting screen.